The present invention relates to a multi-channel pulse width modulation apparatus and a down counter, and more specifically, to a multi-channel pulse width modulation apparatus having high operational reliability, and a down counter used for the multi-channel pulse width modulation apparatus.
Conventionally, in order to increase the speed of exposure processing, an image recording apparatus such as a printer or the like which exposes an image on a photosensitive material on the basis of image data, and transfers and outputs onto regular paper the image recorded on the photosensitive material by the exposure, is provided with a plurality of light emission elements such as an LED chip or an LD used for the exposure and performs exposure corresponding to a plurality of pixels at the same time by the plurality of light emission elements.
This type of image recording apparatus controls each light emission of the plurality of light emission elements by an individual pulse width modulation signal (hereinafter, referred to as a xe2x80x9cPWM signalxe2x80x9d), and the apparatus is generally provided with a multi-channel pulse width modulation apparatus which can generate the same number of PWM signals as that of the light emission elements at the same time.
In a multi-channel pulse width modulation apparatus provided in such an image recording apparatus, either one of the following two methods has been adopted as a setting method of a pulse output timing of each channel, as shown in FIG. 13: a method in which each pulse of the PWM signal is started synchronously to a pixel clock showing one cycle when image recording for one pixel is carried out in a main scanning direction (hereinafter, referred to as an xe2x80x9cedge starting outputxe2x80x9d), and a method in which each pulse is output so that a center of each pulse of the PWM signal is positioned in a vicinity of a central position between each pulse of the pixel clock (hereinafter, referred to as a xe2x80x9ccenter starting outputxe2x80x9d).
In such a multi-channel pulse width modulation apparatus, there has been the problem that sometimes when PWM signals of a plurality of channels start at the same time, a large amount of current flows at the same time into a circuit for generating the PWM signals and the voltage of the power source for supplying the current becomes unstable, whereby operational reliability of the multi-channel pulse width modulation apparatus is considerably deteriorated.
With respect to a multi-channel pulse width modulation apparatus that performs edge starting output, Japanese Patent Application Laid-Open (JP-A) No. 9-23145 discloses as a technology for eliminating the aforementioned problem a technology in which the starting time of each pulse of the PWM signals is fixedly shifted between each channel. However, with respect to a multi-channel pulse width modulation apparatus that performs center starting output, there is no effective technology. In this case, the problem that operational reliability of the multi-channel pulse width modulation apparatus may be considerably deteriorated has been unavoidable.
In other words, in the case of edge starting output, simultaneous starting of the PWM signals of the plurality of channels can be avoided by fixedly shifting the starting time of the PWM signal for each channel by one reference clock, as shown in FIG. 14A.
hence, in the case of center starting output, when the image data corresponding to each PWM signal of, for example, channels 1, 2 and 3 is 2, 2 and 6, respectively, since the image data of channel 1 and channel 2 are equivalent, the start of the PWM signals of channel 1 and channel 2 will be simultaneous in an ordinary center starting output.
Therefore, when the PWM signals are generated so that the center of the pulse of the PWM signal in each channel is shifted between each channel by one standard clock, as shown in FIG. 14B, the start of each PWM signal of channel 1 and channel 2 is shifted by one standard clock, but the start of each PWM signal of channel 1 and channel 3 becomes simultaneous.
When this phenomenon of simultaneous start up occurs in a plurality of channels, the problem that operational reliability may be considerably deteriorated occurs.
In order to solve the above problem, a first object of the present invention is to provide a multi-channel pulse width modulation apparatus which can prevent a decline in operational reliability resulting from a simultaneous start of pulse width modulation signals, and a second object is to provide an inexpensive down counter which can be used for the multi-channel pulse width modulation apparatus.
In order to achieve the first object, a multi-channel pulse width modulation apparatus according to a first aspect of the present invention comprises: a plurality of pulse width modulation signal generators which respectively generate a pulse width modulation signal, and when a timing signal showing a shifted amount of the generation timing of the pulse width modulation signal is inputted thereto, generate a pulse width modulation signal in which the generation timing thereof is shifted corresponding to the timing signal; and a determination section that determines whether or not the pulse width modulation signals from the plurality of pulse width modulation signal generators exceed a predetermined number and become effective at substantially the same time, and on the basis of the results of the determination, generates the timing signals so that the number of pulse width modulation signals that become effective at substantially the same time becomes no greater than the predetermined number, and outputs the timing signals to a corresponding pulse width modulation signal generation section.
According to the multi-channel pulse width modulation apparatus of the first aspect of the present invention, the pulse width modulation signals are respectively generated by the plurality of pulse width modulation signal generation sections, and when the timing signal showing the shifted amount of each generation timing is inputted, pulse width modulation signals whose generation timing is shifted corresponding to the timing signal are generated.
On the other hand, whether or not the pulse width modulation signals from the plurality of pulse width modulation signal generation sections exceed a predetermined number and become effective at substantially the same time is determined by the determination section. On the basis of the results of the determination, the timing signal is generated so that the number of pulse width modulation signals which become effective at substantially the same time becomes no greater than the predetermined number, and is output to the corresponding pulse width modulation signal generation section. By xe2x80x9cbecome effectivexe2x80x9d used herein is meant that the pulse width modulation signal xe2x80x9crisesxe2x80x9d when the pulse width modulation signal is generated in the positive logic, and that the pulse width modulation signal xe2x80x9cdropsxe2x80x9d when the pulse width modulation signal is generated in the negative logic.
Accordingly, the pulse width modulation signals generated respectively by the plurality of pulse width modulation signal generation sections are generated so that the number of pulse width modulation signals that become effective at substantially the same time is no greater than the predetermined number. The predetermined number preferable has as an upper limit a value within a range in which operational reliability of the apparatus is permitted.
In this manner, according to the multi-channel pulse width modulation apparatus of the first aspect of the present invention, whether or not the pulse width modulation signals from the plurality of pulse width modulation signal generation sections exceed a predetermined number and become effective at substantially the same time is determined, and on the basis of the results of the determination, the number of pulse width modulation signals that become effective at substantially the same time is made no greater than the predetermined number. Hence, a decline in operational stability resulting from the pulse width modulation signals becoming effective at substantially the same time can be prevented.
Moreover, the multi-channel pulse width modulation apparatus in a second aspect of the present invention is characterized in that, in the invention of the first aspect, on the basis of the results of the determination, the determination section generates the timing signals so that the pulse width modulation signals do not become effective at substantially the same time and outputs the timing signals to the corresponding pulse width modulation signal generators.
As described above, according to the multi-channel pulse width modulation apparatus of the second aspect of the present invention, the pulse width modulation signals are not made effective at substantially the same time, and hence, it can be reliably prevented that the operational reliability decreases due to the pulse width modulation signals being made effective at substantially the same time.
In this manner, according to the multi-channel pulse width modulation apparatus of the second aspect of the present invention, because the pulse width modulation signals do not become effective at substantially the same time, a decline in operational stability resulting from the pulse width modulation signals becoming effective at substantially the same time can be reliably prevented.
Further, in the multi-channel pulse width modulation apparatus according to a third aspect, the predetermined number is 1.
According to the multi-channel pulse width modulation apparatus of the third aspect, the determination section in the invention of the first aspect determines whether or not the pulse width modulation signals from the plurality of pulse width modulation signal generators exceed 1 and become effective at substantially the same time, and on the basis of the results of the determination, generates the timing signals so that the number of pulse width modulation signals that become effective at substantially the same time becomes no greater than 1, and outputs the timing signals to a corresponding pulse width modulation signal generation section.
In this manner, according to the multi-channel pulse width modulation apparatus of the third aspect, because the plurality of pulse width modulation signals do not become effective at substantially the same time, a decline in operational stability of the apparatus resulting from the pulse width modulation signals becoming effective at substantially the same time can be reliably prevented.
Moreover, in the multi-channel pulse width modulation apparatus according to a fourth aspect, the determination section determines whether or not the time at which the pulse width modulation signals become effective is substantially the same, on the basis of one of: whether or not pulse widths of the pulse width modulation signals that the plurality of pulse width modulation signal generators generate are substantially equivalent; and whether or not scheduled timings indicated by scheduled timing signals are substantially equivalent, with the scheduled timing signals indicating scheduled timings at which the pulse width modulation signals are generated, and being outputted from each pulse width modulation signal generator to the determination section prior to generation of the pulse width modulation signals.
Namely, in the case of center starting output, because the pulse width modulation signals become effective at substantially the same time when the width data values indicating pulse widths of the pulse width modulation signals are substantially equivalent, a determination can be made as to whether or not the pulse width modulation signals become effective at substantially the same time, on the basis of whether or not the width data are equivalent. In this case, because a determination can be made as to whether or not the pulse width modulation signals become effective at substantially the same time without the intervention of the pulse width modulation signal generation section, the determination can be carried out easily and rapidly.
Further, in the pulse width modulation signal generation section, there are many cases in which the timings at which the pulse width modulation signals are generated by the generation section itself are determined in advance. In these cases, each pulse width modulation generator is provided with a function that outputs, prior to the generation of the pulse width modulation signals, to the determination section scheduled timing signals that indicate the scheduled times at which the pulse width modulation signals to be generated are generated. Therefore, on the basis of whether or not the scheduled generation timings indicated by the scheduled timings inputted from each pulse width modulation signal generator are substantially equivalent, the determination section is able to determine whether or not the pulse width modulation signals become effective at substantially the same time. In these cases, because the scheduled timing signals are produced by the pulse width modulation signal generators themselves, the determination section can recognize highly precise scheduled generation timings for the pulse width modulation signals. Consequently, the determination section can determine with high precision whether or not the pulse width modulation signals become effective at substantially the same time.
In this manner, according to the multi-channel pulse width modulation apparatus of the fourth aspect, whether or not the time at which the pulse width modulation signals become effective is substantially the same can be determined on the basis of one of: whether or not pulse widths of the pulse width modulation signals that the plurality of pulse width modulation signal generators generate are substantially equivalent; and whether or not scheduled timings indicated by scheduled timing signals are substantially equivalent, with the scheduled timing signals indicating scheduled timings at which the pulse width modulation signals are generated, and being outputted from each pulse width modulation signal generator to the determination section prior to generation of the pulse width modulation signals. Accordingly, in the former case, determination can be carried out easily and rapidly, and in the latter case, determination can be carried out with high precision.
In order to achieve the first object described above, the multi-channel pulse width modulation apparatus in a fifth aspect of the present invention comprises: a plurality of pulse width modulation signal generators that respectively output a request signal requesting permission to initiate generation of a pulse width modulation signal, and that stop the output of the request signal when an enabling signal indicating permission to initiate generation of the pulse width modulation signal is inputted and initiate generation of the pulse width modulation signal; and an intervening section that outputs enabling signals to corresponding pulse width modulation signal generators when the request signals output from the plurality of pulse width modulation signal generators are inputted and the number of request signals that have become effective at substantially the same time is no greater than a predetermined number, and that outputs enabling signals to a number of pulse width modulation signal generators no greater than the predetermined number when the number of request signals that have become effective at substantially the same time exceeds the predetermined number.
According to the multi-channel pulse width modulation apparatus of the fifth aspect of the present invention, request signals that request permission to start the generation of pulse width modulation signals are respectively output by the plurality of pulse width modulation signal generation sections, and when the enabling signal indicating permission to start the generation of the pulse width modulation signals is inputted, output of the request signal is stopped, whereby generation of the pulse width modulation signals is initiated. When the request signal is output, the request signal may be continuously output or may be repeatedly output for every predetermined time.
In the fifth aspect of the present invention, when the number of request signals that have become effective at substantially the same time is no greater than the predetermined number, enabling signals are output to the pulse width modulation signal generation sections by the meditation portion to which request signals output from the plurality of pulse width modulation signal generation sections are input. When the number of request signals exceeds the predetermined number, the enabling signals are output to a number of pulse width modulation signal generation sections no greater than the predetermined number. By xe2x80x9cbecome effectivexe2x80x9d used herein is meant that the request signal xe2x80x9crisesxe2x80x9d when the request signal is generated in the positive logic, and that the request signal xe2x80x9cdropsxe2x80x9d when the request signal is generated in the negative logic.
Therefore, the pulse width modulation signal generated respectively by the plurality of pulse width modulation signal generation sections are generated so that the number of pulse width modulation signals that become effective at substantially the same time becomes no greater than the predetermined number. The predetermined number preferable has as an upper limit a value within a range in which operational reliability of the apparatus is permitted.
In this manner, according to the multi-channel pulse width modulation apparatus of the fifth aspect of the present invention, with regard to the request signals output from the plurality of pulse width modulation signal generation sections, when the number of request signals that have become effective at substantially the same time exceeds the predetermined number, enabling signals indicating permission to start the generation of the pulse width modulation signals are output a number of pulse width modulation signal generation sections no greater than the predetermined numbers. Therefore, the number of pulse width modulation signals that become effective at substantially the same time can be made no greater than the predetermined number. Hence, a decline in operational stability resulting from the pulse width modulation signals becoming effective at substantially the same time can be prevented.
Moreover, the multi-channel pulse width modulation apparatus in a sixth aspect of the present invention is characterized in that, in the invention of the fifth aspect of the present invention, the intervening section outputs the enabling signals in a predetermined order of priority.
At this time, when a plurality of enabling signals is output by the intervening section, the enabling signals are output in the predetermined order of priority. However, when one enabling signal is output by the intervening section, that is, when the predetermined number is 1, the enabling signal is output only to the pulse width modulation signal generation section having the highest priority ranking.
In this manner, according to the multi-channel pulse width modulation apparatus of the sixth aspect of the present invention, because the enabling signals are output in the predetermined order of priority, the pulse width modulation signals may be set so that do not become effective at substantially the same time. Hence, a decline in operational stability resulting from the pulse width modulation signals becoming effective at substantially the same time can be prevented.
It should be noted that the order of priority may be different for each pulse width modulation signal generator, or a same order of priority may also be present.
A multi-channel pulse width modulation apparatus in a seventh aspect of the present invention is characterized in that, in the invention according to the fifth aspect, the pulse width modulation signal generator respectively include: a conversion portion that obtains conversion data in which complement of 1 in the width data indicating a pulse width of a pulse width modulation signal to be generated is shifted to the right by one bit; and
a pulse generator that generates the pulse width modulation signal by initiating output of the pulse width modulation signal after an elapse of time corresponding to the conversion data has been calculated and stops output of the pulse width modulation signal after an elapse of time corresponding to the width data has been calculated.
In other words, the output mode of the pulse width modulation signal that is a main object of the present invention is the center starting output (see FIG. 13), and the starting time of the output of the pulse width modulation signal in this case is a point in time in which a time obtained by subtracting the time corresponding to half the pulse width of the pulse width modulation signal from the time corresponding to the half cycle of the pixel clock has elapsed since the generation of the pixel clock.
Here, one cycle of the pixel clock is generally substantially equal to the maximum pulse width of the pulse width modulation signal. In this case, the xe2x80x9ctime obtained by subtracting the amount of time corresponding to half the pulse width of the pulse width modulation signal from the amount of time corresponding to the half cycle of the pixel clockxe2x80x9d can be obtained as conversion data in which complement of 1 in the width data showing the pulse width of the pulse width modulation signal is shifted to the right by 1 bit.
The complement of 1 in the width data at this time can be easily obtained by reversing the value of each bit when the width data is expressed by binary notation, and the above-described right shift by one bit can be easily obtained by using the value of a bit other than the least significant bit. Therefore, the xe2x80x9ctime obtained by subtracting the amount of time corresponding to half the pulse width of the pulse width modulation signal from the amount of time corresponding to the half cycle of the pixel clockxe2x80x9d can be obtained by these operations easily and in a short period of time, compared to a case in which the time is obtained by calculation.
In this manner, according to the multi-channel pulse width modulation apparatus of the seventh aspect of the present invention, an effect similar to that of the fifth or sixth aspect can be obtained. Further, conversion data, in which complement of 1 in the width data indicating the pulse width of the pulse width modulation signal to be generated is shifted to the right by 1 bit, is obtained. Output of the pulse width modulation signals is initiated after the elapse of time corresponding to the conversion data has been calculated. Output of the pulse width modulation signals is stopped after the elapse of time corresponding to the width data has been calculated. Accordingly, the pulse width modulation signals are generated. For this reason, the pulse width modulation signals can be obtained easily and in a short period of time.
In the pulse width modulation signal generation section of the multi-channel pulse width modulation apparatus pertaining to the present invention, because a down counter is necessary for the number of channels when the down counter is used, it is preferable that the structural parts of the down counter are as few as possible. By reducing the number of component parts of the down counter, the apparatus can be made inexpensive, and power consumption and noise can be reduced.
Therefore, it is preferable to use an asynchronous counter having fewer component parts than a synchronous counter as the down counter. However, as shown in FIG. 17 and FIG. 18, the conventional asynchronous counter requires two NAND gates (two AND gates when a D-type flip flop preset terminal PR and a clear terminal CL in these figures are both positive logic) for each circuit structure corresponding to one bit.
Taking this into consideration, the down counter of the present invention comprises: a plurality of edge trigger type flip flops that are tandem connected and that each have a preset terminal and a clear terminal; a preset input terminal connected to all of the preset terminals of said plurality of flip flops; a plurality of two-input AND gates whose output terminals are connected to the clear terminals of said plurality of flip flops; a load signal input terminal connected to all of the one side input terminal of said plurality of AND gates; a plurality of data input terminals connected to the other side input terminal of said AND gates, respectively; and a detection circuit for detecting that values held by said plurality of flip flops become all zero and outputting a detection signal.
It should be noted that this structure is a structure when the clear terminal is a positive logic, and that the AND gate pertaining to the present invention becomes a NAND gate when the clear terminal is a negative logic.
In this manner, according to the down counter of the present invention, a plurality of flip-flop preset terminals included in the down counter are connected to a single preset input terminal, whereby the number of AND gates (or NAND gates) corresponding to preset terminals conventionally required is cut back. As a result, the down counter can be produced inexpensively, and power consumption and noise can be reduced.